1. Pre-approvals are not approvals.
2. Contingency clauses can be absurd. It is possible to put in 'subject to the agreement of my partner' without even specifying that your partner is you cat. If there is a contingency clause, they can more than likely wiggle out of it without any problem.
I tried to buy a much less expensive house back in '97. Yes, pre-approval means absolutely nothing. I also asked for additional time, and it was granted.
After the first rejection, the sellers' agent said something about the sellers carrying the financing but that never materialized. I finally pulled out of the deal. My down payment was returned in full.
Pre-approvals say that assuming all else is good, you're OK for the loan. However, things can happen including but not limited to:
-Appraisal insufficient or unacceptable
-Loan officer issued pre-approval without properly calculating a parameter that an underwriter deems unacceptable
-credit re-pulled and credit score drops
-Unacceptable terms of purchase agreement